This invention relates to apparatus and method for salvaging core laminations from the core and windings of an electric motor and more particularly, but not by way of limitation, relates to such apparatus and method for use with elongated electric motors, such as those used with submersible pumps.
Electric motors typically have stators made of a plurality of annular disks, commonly referred to as "laminations." The laminations typically have generally parallel and planar sides and a plurality of slots surrounding the inner periphery of each lamination. In the electric motors used to drive submersible pumps, the laminations are typically inserted in a housing or shell in which they are juxtaposed such that the central openings in the annular laminations form a central passageway for housing a rotor and the slots are aligned to form continuous slots or passageways extending the length of the "core" formed by the laminations. Coil wires or windings are placed in the slots, normally within Teflon.RTM. pen tubes, as is known in the industry.
Prior to 1974, a polyester resin varnish was injected into the slots to secure the windings in the slots and coat the windings. When a motor needed to be rebuilt, the windings were pulled from the slots and the laminations were left in the shell for rewinding.
About 1974, most of the submersible pump industry switched from the oven-cured polyester resin varnish to a chemically-cured or catalyzed epoxy varnish. The epoxy varnish is injected or inducted into the slots and bonds to the edges of the slots and to the windings and thereby holds the windings and the laminations in place. In other words, as well as bonding the windings within the slots, the epoxy varnish also bonds the laminations to the windings and the laminations to one another. The epoxy varnish gained widespread acceptance because it hardens rapidly, more completely fills the slots surrounding the windings, and is more moisture resistant than the polyester resin varnishes. However, it is not possible to pull the windings from the slots when epoxy varnish has been used. The greater strength of the epoxy varnish causes the windings to break and causes damage to the laminations. This is particularly true with the elongated electric motors used to drive submersible pumps, which are commonly 20 to 30 feet in length. The salvage value of the core laminations and windings has encouraged substantial research into methods of economically removing the windings and laminations from electric motors in which the epoxy varnish has been used. (The current market price for new laminations is about 24 cents each and they cost approximately 18 cents each to manufacture. The invention will allow laminations to be salvaged at a cost of approximately 0.015 cents each.) To the knowledge of the applicant, prior to the present invention, an economically viable method and apparatus of doing so has not been available. It is also noteworthy that the efficiency of laminations increases as they are reused.
U.S. Pat. No. 5,001,828 (Missman) discloses an apparatus for removing coil wire from a stator. The Missman apparatus is labor intensive in that a push rod must be positioned over and in alignment with each stator slot and pushed through the stator slot to clear the slot of wire and insulation. There are typically 18 slots in the stator of an electric motor for a submersible pump. U.S. Pat. No. 5,199,159 (Waldsmith) discloses a method for the cryogenic removal of copper wiring from the magnetic core of an electromagnetic machine. Although this method may be acceptable for smaller electric motors, to the best knowledge of the applicant, its economic and technical viability with electric motors as large as those used with submersible pumps has not been demonstrated.
U.S. Pat. No. 4,051,749 (Bell et al.) discloses a cable insulation stripping apparatus used for stripping insulating casing from electrical cable. The apparatus includes a pair of cable clamping assemblies, one of which is adapted to substantially sever a portion of the cable insulation being removed and the other which is used to rigidly clamp around the circumference of the cable to assist in the retention of the cable. This apparatus is not suitable for removing core laminations from an electric motor in that core laminations are not rigid enough to withstand a circumferential surface clamping strong enough to hold against the longitudinal forces necessary to shear core laminations from windings. In the applicant's experience, under such forces the core laminations bend or collapse within the circumferential clamp and the longitudinal forces exerted to remove core laminations from the windings pull the core through the circumferential clamping assembly, thereby bending and destroying the core laminations. Since electrical cable insulation is not normally bonded to the cable insulated, such shearing forces are not a concern in electrical cable insulation stripping apparatus.
Therefore, there is a need for an apparatus and method for salvaging core laminations from the core and windings of an electric motor which is relatively inexpensive, which reduces labor requirements, and which minimizes damage to the windings and core laminations.